CDMA2000 (code division multiple access 2000) is a third-generation (3G) wireless communications standard that uses Code Division Multiple Access (CDMA) to facilitate wireless communications between CDMA base stations and mobile devices. Variants of CDMA2000 include CDMA2000 1x, which provides both voice and data services over a standard CDMA channel, and CDMA2000 Evolution Data-Optimized (1xEV-DO) which is optimized for High Data Rate (HDR) capability. Current versions of the CDMA2000 standards are published and approved by the Telecommunications Industry Association and the International Telecommunication Union.
In a CDMA2000 1x system, communications channels in a forward link signal transmitted by a base station are identified using Walsh codes. A voice user is assigned one of 64 unique Walsh codes, allowing the voice user to receive and decode data on a corresponding traffic channel. A pilot channel, a sync channel and a plurality of paging channels are also identified using Walsh codes, which reduces the number of Walsh codes available for voice communications. In a system implementing the CDMA2000 1x data mode, each user is similarly assigned a unique Walsh code for each assigned channel which may include a fundamental channel (FCH) or a dedicated control channel (DCCH) for data rates up to 9.6 kpbs. If the user's date rate is greater than 9.6 kbps, then the user is further assigned a second Walsh code associated with a supplemental channel.
As all IP mobile networks become more popular, the number of mobile users attempting wireless packet communications could exceed the system capacity which is limited by the 64 Walsh codes that are typically available. Further, during operation, packet data users assigned Walsh codes may be in a control/hold state during short idle periods between packet bursts. These Walsh codes are not available for use by other users during these periods of inactivity.
The 64 Walsh codes used in CDMA2000 systems are mutually orthogonal and were selected to avoid unwanted interference between traffic channel signals transmitted from the same base station. Thus, there are practical limitations associated with adding more Walsh codes. In view of the above, there is a need for an improved system and method for utilizing Walsh codes in wireless communications systems.